The invention relates to rotatable bits, more particularly the invention provides a retainer mechanism for use with both rotatable bits directly mounted in support blocks as well as the wear sleeves used in combination with rotatable bits mounted in support blocks.
Various excavating tools and bits for use therewith are well known in the art. For example, pick type mining bits take the form of an elongated body, round in cross section and symmetrical across the central axis with a cylindrical supporting shank at one end and with the other end generally tapering inwardly to a point in which is mounted a cemented carbide wear resistant element. Such bits, it has been found, will rotate on their axis when properly supported. The rotation is preferably caused by the engagement of the bit with the work and has the advantage of distributing the wear about the periphery of the bit. As a result, the life of the bit is substantially lengthened while the point end of the bit remains sharp.
The portion of the bit immediately rearwardly of the point is usually conical and, as the bit is used and rotates in use, the body of the bit adjacent the hard cemented carbide insert wears away so that the carbide insert remains exposed
In connection with the rotation of the bit in the holder, the bit and holder comprise cooperating, inclined or conical shoulder areas, and these shoulder areas are subjected to substantial loads as the bit is used. Because of the loads involved, the shoulders sometimes wear relatively rapidly. With the bit itself, relatively rapid wear of the shoulder is not particularly important because, at worst, it will not wear away nearly as rapidly as the working point end thereof. Support for the bit, however, is in the form of a block which is usually welded in place on the drive machine and rapid wear of the shoulder on the block is a serious problem because the block is normally expected to remain in good condition for the life of several bits.
It has been found that the use of a metal wear sleeve which supports the shank of the bit while itself, in turn, is supported within the support block has substantially eliminated this problem. Various configurations of support blocks and sleeves are known in the art. An example of this can be found in Reissue U.S. Pat. No. 29,900, which is assigned to the assignee of the present invention and which is incorporated herein by reference.
While such tools operate in a highly efficient manner, it is nevertheless the case that, in at least certain formations, the tool is exposed to nonuniform impact conditions when working. These conditions result in a tendency for the tool to be subjected to a widely varying load in the axial direction with the tool even tending at times to be thrust forwardly or to tend to jump forwardly in the supporting block.
The tools are normally retained in the blocks by snap rings or the like mounted on the tool shank at the rear end of the block and, while snap rings are effective for retaining tools in the block, the aforementioned operating conditions cause the snap ring to engage the back of the block and to wear off the back of the block to the point that the tools develop a substantial amount of freedom of movement in the axial direction in the support block provided therefor. A variety of keeper arrangements are known in the art and are used to retain the cutting tool within the block or the wear sleeve within the block. Examples of this can be seen in U.S. Pat. Nos. 3,830,321 and 3,820,848, both of which are assigned to the assignee of the present invention and incorporated herein by reference.
With the foregoing in mind, it is a primary object of the present invention to provide an improved mining tool of the nature referred to in which the problems referred to above are substantially diminished.
Another object of the invention is the provision of a keeper arrangement for retaining a rotary mining tool in a support block which substantially eliminates erratic axial movements of the tool in the block.
It is yet another object of the invention to provide a keeper arrangement for retaining a rotating wear sleeve in a support block.
It is yet another object of this invention to provide the combination of a mining tool support block and keeper arrangement therefor for retaining the tool in the block in which substantially all of the relatively movable surfaces of the tool and block are protected from fine abrasive material developed during working operations.
It remains another object of this invention to provide keeper arrangement which facilitates both the installation and removal of mining bits and wear sleeves from support blocks.